CN105627107A - Modal acoustic emission time-frequency locating method adopting single sensor for fluid pipeline - Google Patents

Abstract

The invention discloses a modal acoustic emission time-frequency locating method adopting a single sensor for a fluid pipeline. The method comprises the steps of 1, picking up acoustic emission signals of pipeline leakage through the single acoustic emission sensor at any contactable terminal of the leaking pipeline; 2, carrying out time-frequency analysis on the acoustic emission signals of leakage for obtaining a time-frequency spectrum; 3, extracting time information and frequency information corresponding to three peaks of the time-frequency spectrum of the leakage signals; 4, obtaining the time differences between any two modal signals according to the three kinds of peak time, substituting three kinds of peak frequency into corresponding frequency dispersion curves of three modes and obtaining the sound speeds of the signals of the three modes; 5, obtaining the positions of three leakage points according to the obtained three time differences and sound speeds and averaging the leakage points. According to the method, just one acoustic emission sensor is needed for determining the position of the leakage point, the operation is easy and convenient, and the method can be conveniently applied to engineering; pipeline leakage can be accurately located on the condition that leakage cannot be located because of multiplex modes and the frequency dispersion characteristic.

Description

Fluid line single-sensor Modal Acoustic Emission time-frequency localization method

Technical field

The invention belongs to pipeline leakage testing field, be specifically related to a kind of fluid line single-sensor Modal Acoustic Emission time-frequency localization method.

Background technology

Pipeline is widely used in the fluid transport such as natural gas, oil as the efficient fluid mode of movement easily of one. Due to nature or artificial origin: pipeline is aging, corrosion, and geology settles, and construction lack of standardization etc., pipe leakage happens occasionally. Gas pipe leakage causes the wasting of resources, environmental pollution, even blast, the serious accident such as poisoning, causes serious threat to the lives and properties of people. Therefore, the harm that fluid line Leak Detection location technology causes for reducing pipe leakage is very necessary.

Acoustic emission is increasingly subject to the concern of people as a kind of lossless detection method in-service in real time in fluid line Leak Detection. Generally, acoustic emission pipeline leakage testing needs the Continuous Acoustic Emission that two the acoustic emission sensors acquisition leakages of at least two contact point installation at tube wall cause to realize the Leak Detection to whole pipeline. Chinese patent (CN103062628A) discloses a kind of buried pipeline leakage detecting and locating method based on acoustic emission, overcome the deficiency of existing leak detection technology, combined with wavelet transformed de-noising and correlation analysis, it is achieved that to the real-time nondestructive testing in service of buried pipeline. The method is applied to the test pipe that length is 6 meters, utilize two acoustic emission sensors to obtain two-way acoustic emission signal on the tube wall of leakage point two ends simultaneously, utilizing cross-correlation that two-way acoustic emission signal carries out time delay to estimate to determine leak position, position error is 15.2%. Adopt wavelet transform denoising can reduce cross-correlation position error when detecting duct length and being less, but position error is still more than 5%. This is primarily due to cross-correlation positioning method and is built upon leakage acoustic emission signal along pipeline with under the premise of invariable sonic transmission, but actually pipeline leakage acoustic emission signals has broadband, frequency dispersion, the characteristic such as multi-modal, different mode has frequency dispersion in various degree and different transmission speeds, namely leakage acoustic emission spread speed in the duct is closely related with frequency and modality type, and invariable sound degree is difficult to obtain. If directly the acoustic emission signal gathered being carried out correlation analysis locating leaks, the dependency of signal is weak, and time delay estimation difference is big; The velocity of sound can only take the meansigma methods of a certain mode guided wave speed in frequency range on the other hand, and these 2 can be caused relatively gross leak position error. Therefore big based on the acoustic emission pipeline leakage detection method position error of cross-correlation, be not suitable for the situation that the serious and constant velocity of sound of frequency dispersion is difficult to determine. Then, Chinese patent (CN104747912A) discloses a kind of fluid-transporting tubing leakage acoustic emission time-frequency localization method, first acoustic emission signal leakage two ends gathered carries out cross-correlation analysis, then cross-correlation function is carried out time frequency analysis to determine time delay and corresponding frequency information, thus realizing time-frequency location. The method overcome the problem that the position error caused because of leakage acoustic emission signal frequency dispersion is big, what its essence adopted is the time-frequency localization method of the cross-correlation function of a kind of single dominant mode signal, but actual leakage acoustic emission signal is multi-modal signal (mode of flexural vibration, torsion mode, longitudinal mode and fluid dominant mode), thus can cause that leakage signal degree of correlation when carrying out cross-correlation analysis that leakage two ends gather is weak so that time-frequency position error is bigger mutually. It addition, the method need nonetheless remain for two sensors could realize the location of leakage point, so a degree of inconvenience can be caused in engineer applied.

Summary of the invention

In view of this, it is an object of the invention to provide a kind of fluid line single-sensor Modal Acoustic Emission time-frequency localization method.

It is an object of the invention to be achieved through the following technical solutions, a kind of fluid line single-sensor Modal Acoustic Emission time-frequency localization method, comprise the following steps:

Step 1) adopt single acoustic emission sensor arbitrarily can pick up pipeline leakage acoustic emission signals by contact terminal at leakage pipe;

Step 2) to leakage acoustic emission signal carry out time frequency analysis obtain time-frequency spectrum;

Step 3) extract temporal information corresponding to three time-frequency spectrum peak values and the frequency information of leakage signal, three described time-frequency spectrum peak values are corresponding mode of flexural vibration, longitudinal mode and fluid dominant mode respectively;

Step 4) utilize three time to peaks to ask for the time difference of any both modalities which signal, utilize the dispersion curve that three kinds of crest frequencies substitute into three kinds of corresponding mode to obtain the velocity of sound of three kinds of mode signals;

Step 5) obtain three kinds of leakage point positions according to required three kinds of time differences and the velocity of sound, and it is averaging obtains leak position more accurately.

Further, described any both modalities which signal time difference is the time difference of any two time-frequency spectrum peak value.

Further, the velocity of sound of described mode signals obtains by frequency information corresponding for the peak value of corresponding mode time-frequency spectrum substitutes into the dispersion curve of corresponding mode.

Further, described localization method particularly as follows:

The leakage acoustic emission signal that described acoustic emission sensor picks up at tube wall is expressed as:

X (t)=F (t)+L (t)+f (t) (1)

Wherein, X (t) represents leakage acoustic emission signal, and F (t) represents mode of flexural vibration signal, and L (t) represents longitudinal mode signal, and f (t) is fluid dominant mode signal;

Leakage acoustic emission signal X (t) is carried out time frequency analysis is:

$\begin{array}{c}{C}_x(t,\mathrm{\ω})=TF\[X\left(t\right)\]=TF\[F\left(t\right)+L\left(t\right)\]=TF\[F\left(t\right)\]+TF\[L\left(t\right)\]+TF\[f\left(t\right)\]\\ =C_F(t_F,{\mathrm{\ω}}_F)+C_L(t_L,{\mathrm{\ω}}_L)+C_f(t_f,{\mathrm{\ω}}_f)\end{array}---\left(2\right)$

Wherein, TF is time frequency analysis operator, C_x��C_F��C_LAnd C_fRepresent the time-frequency spectrum of leakage signal, mode of flexural vibration, longitudinal mode and fluid dominant mode, t, t respectively_F��t_L��t_fRepresent the temporal information of leakage signal, mode of flexural vibration, longitudinal mode and fluid dominant mode time-frequency spectrum, ��, �� respectively_F����_LAnd ��_fRepresent the frequency information of leakage signal, mode of flexural vibration, longitudinal mode and fluid dominant mode time-frequency spectrum respectively;

Then corresponding time of three peak values and frequency are represented by:

[��_F0,t_F0]=argmaxC_F(t_F,��_F)(3)

[��_L0,t_L0]=argmaxC_L(t_L,��_L)(4)

[��_f0,t_f0]=argmaxC_f(t_f,��_f)(5)

Wherein, ��_F0����_L0And ��_f0It is the frequency information that mode of flexural vibration, longitudinal mode are corresponding with the peak value of the time-frequency spectrum of fluid dominant mode signal respectively, t_F0��t_L0And t_f0It is the temporal information that mode of flexural vibration, longitudinal mode are corresponding with the peak value of the time-frequency spectrum of fluid dominant mode signal respectively.

Further, by ��_F0����_L0����_f0Namely the dispersion curve substituting into mode of flexural vibration, longitudinal mode and fluid dominant mode respectively can determine that the corresponding velocity of sound is C_F��C_LAnd C_f;

The time difference that any both modalities which signal causes because of speed difference is:

��_FL=t_F0-t_L0(6)

��_fL=t_f0-t_L0(7)

��_fF=t_f0-t_F0(8)

Wherein, ��_FL����_fLAnd ��_fFRespectively the time of advent before mode of flexural vibration and longitudinal mode, fluid dominant mode and longitudinal mode, fluid dominant mode and mode of flexural vibration is poor.

Further, leakage point to the distance of sensor is

$L_{01}=\frac{c_L{c}_F}{c_L-c_F}{\mathrm{\τ}}_{FL}---\left(12\right)$

$L_{02}=\frac{c_L{c}_f}{c_L-c_f}{\mathrm{\τ}}_{fL}---\left(13\right)$

$L_{03}=\frac{c_F{c}_f}{c_F-c_f}{\mathrm{\τ}}_{fF}---\left(14\right)$

Wherein, L₀₁, L₀₂, L₀₃Respectively adopt the position of the leakage point that mode of flexural vibration and longitudinal mode, fluid dominant mode and longitudinal mode, speed difference between fluid longitudinal mode and mode of flexural vibration obtain; Then

$\stackrel{\‾}{L}=\frac{L_{01}+L_{02}+L_{03}}{3}---\left(15\right)$

Wherein,Expression adopts the leakage point meansigma methods to the spacing of sensor of modality combinations calculating three kinds different.

Owing to have employed technique scheme, present invention have the advantage that: compared with traditional double sensor leakage localization method, present invention only requires an acoustic emission sensor and namely can determine that the position of leakage point, easy and simple to handle, it is simple to engineer applied; The present invention proposes a kind of Modal Acoustic Emission time-frequency localization method simultaneously, it is possible to cause that pipe leakage is accurately positioned when cannot position by leakage at multi-modal, Dispersion.

Accompanying drawing explanation

In order to make the object, technical solutions and advantages of the present invention clearly, below in conjunction with accompanying drawing, the present invention is described in further detail, wherein:

Fig. 1 is pipeline three-dimensional coordinate figure;

Fig. 2 is single-sensor leakage positioning principle figure.

Detailed description of the invention

Below with reference to accompanying drawing, the preferred embodiments of the present invention are described in detail; Should be appreciated that preferred embodiment is only for illustrating the present invention, rather than in order to limit the scope of the invention.

The acoustic emission signal that pipe leakage produces is broken down into the mode signals of number of different types along pipeline when transmitting. Along with the increase Modal Acoustic Emission signal of transmission range is decayed therewith, and the more high signal attenuation of frequency is more big, therefore adopts low frequency signal (< 100kHz) to carry out pipe leakage acoustic emission detection. Fluid line is considered as the cylindrical housings composite construction being made up of the medium of tube fluid, tube wall and pipeline external medium three layers different attribute, low frequency leakage acoustic emission signal only encourages modality type four kinds basic when transmitting in this cylindrical housings composite construction: mode of flexural vibration, torsion mode, longitudinal mode and fluid dominant mode, wherein mode of flexural vibration, torsion mode and longitudinal mode mainly transmit in the pipe wall, and fluid dominant mode is then the compressional wave of transmission in fluid. The three-dimensional coordinate of fluid line is as shown in Figure 1, mode of flexural vibration only produces radial displacement and circumferentially displaced, torsion mode only produces circumferentially displaced, and longitudinal mode mainly produces axial displacement and radial displacement, and fluid dominant mode is radial displacement and the axial displacement that fluid compressional wave mainly causes tube wall. The vertical tube wall of acoustic emission sensor is arranged on pipeline, its piezoelectric sensing element adopted is only sensitive to the axial displacement of tube wall and radial displacement, and to circumferentially displaced insensitive, described acoustic emission sensor is mainly mode of flexural vibration signal, longitudinal mode signal and fluid dominant mode in the leakage signal that tube wall picks up, it is possible to be expressed as:

X (t)=F (t)+L (t)+f (t) (1)

Wherein, X (t) represents the leakage signal that acoustic emission sensor picks up, and F (t) represents mode of flexural vibration signal, and L (t) represents longitudinal mode signal, and f (t) is fluid dominant mode signal.

Leakage acoustic emission signal X (t) that single-sensor is picked up carries out time frequency analysis and is:

$\begin{array}{c}{C}_x(t,\mathrm{\&omega;})=TF\&lsqb;X\left(t\right)\&rsqb;=TF\&lsqb;F\left(t\right)+L\left(t\right)\&rsqb;=TF\&lsqb;F\left(t\right)\&rsqb;+TF\&lsqb;L\left(t\right)\&rsqb;+TF\&lsqb;f\left(t\right)\&rsqb;\\ =C_F(t_F,{\mathrm{\&omega;}}_F)+C_L(t_L,{\mathrm{\&omega;}}_L)+C_f(t_f,{\mathrm{\&omega;}}_f)\end{array}---\left(2\right)$

Wherein TF is time frequency analysis operator, which represent all methods of existing time frequency analysis, C_x��C_F��C_LAnd C_fRepresent the time-frequency spectrum of leakage signal, mode of flexural vibration, longitudinal mode and fluid dominant mode, t, t respectively_F��t_L��t_fRepresent the temporal information of leakage signal, mode of flexural vibration, longitudinal mode and fluid dominant mode time-frequency spectrum, ��, �� respectively_F����_LAnd ��_fRepresent the frequency information of leakage signal, mode of flexural vibration, longitudinal mode and fluid dominant mode time-frequency spectrum respectively. Can be seen that the time-frequency spectrum essence to leakage signal is the time-frequency spectrum sum of three kinds of different modalities signals from formula (2).

The transmission speed of three kinds of different modalities signals there are differences, so temporal information corresponding to the peak value of the time-frequency spectrum of three kinds of mode mixed signals will there are differences, thus causing that the time-frequency spectrum of leak data exists three obvious peak values. Wherein corresponding time of three peak values and frequency are represented by:

[��_F0,t_F0]=argmaxC_F(t_F,��_F)(3)

[��_L0,t_L0]=argmaxC_L(t_L,��_L)(4)

[��_f0,t_f0]=argmaxC_f(t_f,��_f)(5)

Wherein, ��_F0����_L0And ��_f0It is the frequency information that mode of flexural vibration, longitudinal mode are corresponding with the peak value of the time-frequency spectrum of fluid dominant mode signal respectively, t_F0��t_L0And t_f0It is the temporal information that mode of flexural vibration, longitudinal mode are corresponding with the peak value of the time-frequency spectrum of fluid dominant mode signal respectively. By the �� in formula (3-5)_F0����_L0����_f0Namely the dispersion curve substituting into mode of flexural vibration, longitudinal mode and fluid dominant mode respectively can determine that the corresponding velocity of sound is C_F��C_LAnd C_f, the time difference that any both modalities which signal causes because of speed difference is

��_FL=t_F0-t_L0(6)

��_fL=t_f0-t_L0(7)

��_fF=t_f0-t_F0(8)

Wherein, ��_FL����_fLAnd ��_fFRespectively the time of advent before mode of flexural vibration and longitudinal mode, fluid dominant mode and longitudinal mode, fluid dominant mode and mode of flexural vibration is poor.

As illustrated in fig. 2, it is assumed that the leakage signal of known two kinds of different modalities time from leakage point to sensor transmissions and the velocity of sound respectively (t₁,c₁), (t₂,c₂), also assume that leak position is L to the distance of sensing station, then:

c₁t₁=c₂t₂=L (9)

t₁-t₂=�� (10)

From formula (9) (10)

$L=\frac{c_1{c}_2}{c_2-c_1}\mathrm{\&tau;}---\left(11\right)$

The velocity of sound in formula (3-8) and time difference then substitute into formula (11) leakage point can be obtained to the distance of sensor be

$L_{01}=\frac{c_L{c}_F}{c_L-c_F}{\mathrm{\&tau;}}_{FL}---\left(12\right)$

$L_{02}=\frac{c_L{c}_f}{c_L-c_f}{\mathrm{\&tau;}}_{fL}---\left(13\right)$

$L_{03}=\frac{c_F{c}_f}{c_F-c_f}{\mathrm{\&tau;}}_{fF}---\left(14\right)$

Wherein, L₀₁, L₀₂, L₀₃Respectively adopt the position of the leakage point that mode of flexural vibration and longitudinal mode, fluid dominant mode and longitudinal mode, speed difference between fluid longitudinal mode and mode of flexural vibration obtain.

Through type (12-14) all can calculate the position of pipe leakage point, is finally undertaken three kinds of results being averaging the error reducing leakage location further, then

$\stackrel{\&OverBar;}{L}=\frac{L_{01}+L_{02}+L_{03}}{3}---\left(15\right)$

Wherein,Expression adopts the leakage point meansigma methods to the spacing of sensor of modality combinations calculating three kinds different.

Modal Acoustic Emission time-frequency localization method of the present invention, it is particularly useful for natural gas, oil, supplies water and other fluid-transporting tubings are when because adopting single-sensor that leakage point is accurately positioned leakage acoustic emission signal frequency dispersion, multi-modal characteristic cause being difficult to position. The thought of this localization method also apply be applicable in the acoustic emission source location of other structures (such as plate and shell structure) simultaneously.

The foregoing is only the preferred embodiments of the present invention, be not limited to the present invention, it is clear that the present invention can be carried out various change and modification without deviating from the spirit and scope of the present invention by those skilled in the art. So, if these amendments of the present invention and modification belong within the scope of the claims in the present invention and equivalent technologies thereof, then the present invention is also intended to comprise these change and modification.

Claims (6)

1. a fluid line single-sensor Modal Acoustic Emission time-frequency localization method, it is characterised in that: comprise the following steps:

Step 1) adopt single acoustic emission sensor arbitrarily can pick up pipeline leakage acoustic emission signals by contact terminal at leakage pipe;

Step 2) to leakage acoustic emission signal carry out time frequency analysis obtain time-frequency spectrum;

Step 3) extract temporal information corresponding to three time-frequency spectrum peak values and the frequency information of leakage signal, three described time-frequency spectrum peak values are corresponding mode of flexural vibration, longitudinal mode and fluid dominant mode respectively;

Step 4) utilize three time to peaks to ask for the time difference of any both modalities which signal, utilize the dispersion curve that three kinds of crest frequencies substitute into three kinds of corresponding mode to obtain the velocity of sound of three kinds of mode signals;

Step 5) obtain three kinds of leakage point positions according to required three kinds of time differences and the velocity of sound, and it is averaging obtains leak position more accurately.

2. fluid line single-sensor Modal Acoustic Emission time-frequency localization method according to claim 1, it is characterised in that: described any both modalities which signal time difference is the time difference of any two time-frequency spectrum peak value.

3. fluid line single-sensor Modal Acoustic Emission time-frequency localization method according to claim 1, it is characterised in that: the velocity of sound of described mode signals obtains by frequency information corresponding for the peak value of corresponding mode time-frequency spectrum substitutes into the dispersion curve of corresponding mode.

4. fluid line single-sensor Modal Acoustic Emission localization method according to claim 1, it is characterised in that: described localization method particularly as follows:

The leakage acoustic emission signal that described acoustic emission sensor picks up at tube wall is expressed as:

X (t)=F (t)+L (t)+f (t) (1)

Wherein, X (t) represents leakage acoustic emission signal, and F (t) represents mode of flexural vibration signal, and L (t) represents longitudinal mode signal, and f (t) is fluid dominant mode signal;

Leakage acoustic emission signal X (t) is carried out time frequency analysis is:

C_x(t, ��)=TF [X (t)]=TF [F (t)+L (t)]=TF [F (t)]+TF [L (t)]+TF [f (t)]

(2)

=C_F(t_F,��_F)+C_L(t_L,��_L)+C_f(t_f,��_f)

Wherein, TF is time frequency analysis operator, C_x��C_F��C_LAnd C_fRepresent the time-frequency spectrum of leakage signal, mode of flexural vibration, longitudinal mode and fluid dominant mode, t, t respectively_F��t_L��t_fRepresent the temporal information of leakage signal, mode of flexural vibration, longitudinal mode and fluid dominant mode time-frequency spectrum, ��, �� respectively_F����_LAnd ��_fRepresent the frequency information of leakage signal, mode of flexural vibration, longitudinal mode and fluid dominant mode time-frequency spectrum respectively;

Then corresponding time of three peak values and frequency are represented by:

[��_F0,t_F0]=argmaxC_F(t_F,��_F)(3)

[��_L0,t_L0]=argmaxC_L(t_L,��_L)(4)

[��_f0,t_f0]=argmaxC_f(t_f,��_f)(5)

Wherein, ��_F0����_L0And ��_f0It is the frequency information that mode of flexural vibration, longitudinal mode are corresponding with the peak value of the time-frequency spectrum of fluid dominant mode signal respectively, t_F0��t_L0And t_f0It is the temporal information that mode of flexural vibration, longitudinal mode are corresponding with the peak value of the time-frequency spectrum of fluid dominant mode signal respectively.

5. fluid line single-sensor Modal Acoustic Emission time-frequency localization method according to claim 4, it is characterised in that: by ��_F0����_L0����_f0Namely the dispersion curve substituting into mode of flexural vibration, longitudinal mode and fluid dominant mode respectively can determine that the corresponding velocity of sound is C_F��C_LAnd C_f;

The time difference that any both modalities which signal causes because of speed difference is:

��_FL=t_F0-t_L0(6)

��_fL=t_f0-t_L0(7)

��_fF=t_f0-t_F0(8)

Wherein, ��_FL����_fLAnd ��_fFRespectively the time of advent before mode of flexural vibration and longitudinal mode, fluid dominant mode and longitudinal mode, fluid dominant mode and mode of flexural vibration is poor.

6. fluid line single-sensor Modal Acoustic Emission localization method according to claim 5, it is characterised in that: leakage point to the distance of sensor is

$L_{01}=\frac{c_L{c}_F}{c_L-c_F}{\mathrm{\&tau;}}_{FL}---\left(12\right)$

$L_{02}=\frac{c_L{c}_f}{c_L-c_f}{\mathrm{\&tau;}}_{fL}---\left(13\right)$

$L_{03}=\frac{c_F{c}_f}{c_F-c_f}{\mathrm{\&tau;}}_{fF}---\left(14\right)$

Wherein, L₀₁, L₀₂, L₀₃Respectively adopt the position of the leakage point that mode of flexural vibration and longitudinal mode, fluid dominant mode and longitudinal mode, speed difference between fluid dominant mode and mode of flexural vibration obtain; Then

$\stackrel{\&OverBar;}{L}=\frac{L_{01}+L_{02}+L_{03}}{3}---\left(15\right)$

Wherein,Expression adopts the leakage point meansigma methods to the spacing of sensor of modality combinations calculating three kinds different.